1. Field of the Invention
The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to an integrated circuit package.
2. Description of the Related Art
Trends in modern integrated circuitry are generally towards smaller size and higher density. This has resulted in the requirement to fit a large number of bond pads (I/O pads) in a relatively small area of the integrated circuit, sometimes called the semiconductor chip.
To route electrical signals to and from the integrated circuit, the bond pads of the integrated circuit were electrically connected to traces on a substrate. However, since the traces were generally larger in size and pitch, i.e., spacing, than the bond pads, the number of traces which could be formed directly adjacent to the integrated circuit was limited.
One technique for overcoming the size and pitch limitations of the traces was to form the traces at a significant distance from the integrated circuit. However, this caused the length of the bond wires extending between the bond pads of the integrated circuit and the corresponding traces to be relatively long. Long bond wires were particularly problematic during the subsequent plastic encapsulation transfer molding process where the integrated circuit, the bond wires, and the substrate were transfer molded into a plastic encapsulate to form the finished integrated circuit package.
More particularly, during the plastic encapsulation transfer molding process, the plastic encapsulate was caused to flow around the integrated circuit, the bond wires, and substrate. This flow of plastic encapsulate against the bond wires caused: (1) the bond wires to become disconnected from the bond pads of the integrated circuit or from the traces; (2) caused the bond wires to break; and/or (3) caused the bond wires to move and short one another. This phenomena is called xe2x80x9cwire sweepxe2x80x9d.
In the event a plastic encapsulation injection molding process was used, wire sweep was even more problematic. Generally, the plastic encapsulate was injected around the integrated circuit, the bond wires and the substrate at a higher pressure in a plastic encapsulation injection molding process than in a plastic encapsulation transfer molding process. Due to this higher pressure, more force was exerted against the bond wires, which were susceptible to wire sweep.
To avoid wire sweep, the bond wires were supported by an intermediate section between the bond pads of the integrated circuit and the traces.
Rostoker, U.S. Pat. No. 5,753,970, which is herein incorporated by reference in its entirety, teaches a lead support structure which supported a bond wire at a point along its length such that the bond wire was mechanically constrained and could not short to adjacent bond wires (see lead support structures 700a, 700b, 700c of FIGS. 9a, 9b, 9c, respectively, of Rostoker). However, providing and attaching such a lead support structure to the substrate was relatively labor-intensive and complex and thus significantly added to the cost of the integrated circuit package.
Typically, each trace was aligned with the specific bond pad on the integrated circuit to which the trace was to be connected. The bond pads on the integrated circuit were connected to the traces in the same order that the bond pads were position on the integrated circuit. However, in certain instances, it was desirable to allow for cross-over connections between the bond pads and the traces. Generally, a cross-over connection is a connection between a bond pad and a trace which is not directly aligned with the bond pad.
Gow, 3Rd. et al., U.S. Pat. No. 5,168,368, which is herein incorporated by reference in its entirety, teaches a bridge which was bonded to a first set of fingers of a lead frame. The bridge was located between the integrated circuit and a second set of fingers. To form a cross-over connection, a bond wire extending between a bond pad and a finger of the second set of fingers was intermediately bonded to the bridge above the first set of fingers. In this manner, the bond wire was crossed over fingers of the first set of fingers. However, providing and attaching such a bridge was relatively labor-intensive and complex and thus significantly added to the cost of the integrated circuit package.
Thus, in both Rostoker and Gow, 3Rd. et al., an intermediate bonding structure was provided between the bond pads and traces (fingers) to reduce the unsupported length of the bond wires and thus avoid wire sweep. However, the intermediate bonding structures had to be fabricated separately and attached to the package during assembly which, as set forth above, was relatively labor-intensive and complex and thus significantly added to the cost of integrated circuit package.
In accordance with the present invention, a plastic encapsulated integrated circuit package having a large number of traces is presented. To allow the required large number of traces to be formed, the traces are spaced a significant distance from the integrated circuit. Bond pads of the integrated circuit are electrically connected to corresponding traces by corresponding long wires. Of importance, the long wires are not susceptible to wire sweep during the plastic encapsulation transfer molding process used to form the package body.
The long wires are intermediately bonded to intermediate bonding pads between the integrated circuit and the traces. Of importance, the distance between the bond pads of the integrated circuit and the intermediate bonding pads is sufficiently small such that looped portions of the long wires, which extend between the bond pads of the integrated circuit and the intermediate bonding pads, are not susceptible to wire sweep.
Of further importance, surface runner portions of the long wires, which extend between the intermediate bonding pads and the traces, extend along and contact the upper surface of the substrate and so are also not susceptible to wire sweep. More particularly, during the plastic encapsulation transfer molding process, the plastic encapsulate flows over the surface runner portions instead of around the surface runner portions. This, in turn, causes the plastic encapsulate to exert much less force on the surface runner portions than if the surface runner portions were suspended above the upper surface of the substrate.
Since the surface runner portions have much less force exerted on them during the plastic encapsulation transfer molding process, the surface runner portions can be formed of a greater length than conventional suspended bond wires.
Recall that in the prior art, the unsupported sections of the bond wires extending between the bond pads and the traces were suspended above the substrate. During the plastic encapsulation transfer molding process, the plastic encapsulate flowed around these unsupported sections of bond wires, which were susceptible to wire sweep.
For this reason, each unsupported section of bond wire had to be no greater than the maximum allowable wire bond length. Thus, even using an intermediate bonding structure of the prior art, the allowable distance between the bond pads and the traces was equal to approximate twice the maximum allowable wire bond length.
However, the distance between the bond pads and the traces needs to be greater than twice the maximum allowable wire bond length in certain instances, for example, when a large number of traces are required.
To increase the distance between the bond pads and the traces, additional intermediate bonding structures were provided. However, these additional intermediate bonding structures had to be fabricated separately and attached to the package during assembly which further added to the cost of the integrated circuit package.
Advantageously, by essentially eliminating the susceptibility of the surface runner portions to wire sweep, the distance between the bond pads and the traces can be much greater than twice the maximum allowable wire bond length. Thus, use of the long wires in accordance with the present invention is well suited for applications in which the traces are at a significant distance from the bond pads, for example, when a large number of the traces are required.
Advantageously, the intermediate bonding pads are formed during the normal processing of the substrate, e.g., during the formation of the traces. Since the intermediate bonding pads are formed during the normal processing of the substrate, there are no additional procedures or materials required for the intermediate bonding pads. Accordingly, there is essentially no cost associated with the intermediate bonding pads.
Recall that in the prior art, an intermediate bonding structure was provided between the bond pads and traces (fingers) to reduce the unsupported length of the bond wires and thus avoid wire sweep. However, the intermediate bonding structures had to be fabricated separately and attached to the package during assembly, which was relatively labor-intensive and complex, and thus significantly added to the cost of the integrated circuit package. Accordingly, the package in accordance with the present invention is fabricated at a lower cost than an integrated circuit package of the prior art.
In an alternative embodiment, a lower long wire electrically connects a first bond pad to a first trace. An upper long wire electrically connects a second bond pad to a second trace. To make the electrical connection between the second bond pad and the second trace, the upper long wire has to cross over the lower long wire. To allow the upper long wire to cross over the lower long wire, a crossover portion of the upper long wire is attached to a first jumper pad and a second jumper pad and extends over the lower long wire. In this manner, the upper long wire crosses over the lower long wire.
Alternatively, to allow the upper long wire to cross over the lower long wire, a crossover portion of the upper long wire is a trace electrically connected to the first jumper pad and the second jumper pad. This trace extends under the lower long wire. In this manner, the upper long wire extends under the lower long wire to form a crossover connection over the lower long wire.
Recall that in the prior art, a bridge was mounted above a first set of fingers. To form a crossover connection, a bond wire was extended between a bond pad and the bridge and was intermediately bonded to the bridge. The bond wire was then extended from the bridge to a finger of a second set of fingers. In this manner, the bond wire was crossed over fingers of the first set of fingers. However, providing and attaching such a bridge was relatively labor-intensive and complex and thus significantly added to the cost of the integrated circuit package.
Advantageously, the jumper pads in accordance with the present invention are formed during the normal processing of the substrate, e.g., during the formation of the traces. Since the jumper pads are formed during the normal processing of the substrate, there are no additional procedures or materials required for the jumper pads. Accordingly, there is essentially no cost associated with the jumper pads or the crossover connection of the upper long wire over the lower long wire.
In one embodiment, a plastic encapsulated integrated circuit package includes a substrate having a first surface with a die attach area and an electrically conductive trace formed thereon. An intermediate bonding pad between the die attach area and the trace is also on the first surface of the substrate.
In another embodiment, a plastic encapsulated integrated circuit package includes a substrate having a first surface with a die attach area. An electronic component has a first surface attached to the die attach area, the electronic component having a second surface. A first bond pad and a second bond pad are on the second surface of the electronic component. A first bond wire is electrically connected to the first bond pad. A first jumper pad and a second jumper pad are on the first surface of the substrate. A crossover portion extends between and electrically connects the first jumper pad and the second jumper pad. The crossover portion forms a crossover connection with respect to the first bond wire.
Also in accordance with the present invention, a method includes forming a first trace and an intermediate bonding pad on a first surface of a substrate. An electronic component is attached to the first surface of the substrate, the electronic component have a first bond pad thereon. The first bond pad is electrically connected to the first trace by a first bond wire attached to the intermediate bonding pad.
These and other features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.